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A burr mill, or burr grinder, is a mill used to grind hard, small food products between two revolving abrasive surfaces separated by a distance usually set by the user. When the two surfaces are set far apart, the resulting ground material is coarser, and when the two surfaces are set closer together, the resulting ground material is finer and smaller. Often, the device includes a revolving screw that pushes the food through. It may be powered electrically or manually.
Burr mills do not heat the ground product by friction as much as blade grinders (“choppers”), and produce particles of a uniform size determined by the separation between the grinding surfaces.
Food burr mills are usually manufactured for a single purpose: coffee beans, dried peppercorns, coarse salt, spices, or poppy seeds, for example.[3] Coffee mills for volume consumption are usually powered by electric motors, but fast and precise manual mills have experienced an uptick in popularity in the 2020s for individual-serving pour-over and espresso. Domestic pepper, salt, and spice mills, used to sprinkle a little seasoning on food, are usually operated manually, sometimes by a battery-powered motor.
The uniform particle size and variable settings of a burr grinder[4] make it well-suited for coffee preparation, as different methods of coffee preparation require different size grinds. The size of the grind is determined by the width between the two burrs, into which the coffee beans fall and are ground a few at a time. A finer grind allows a larger surface area to come into contact with the water, which yields a more complete extraction of caffeine and flavor.The grind spectrum ranges from Turkish coffee and espresso on the finer end to a French press and cold brew extraction on the coarse/extra coarse end, with pour-overs and drip coffee in the medium-fine to medium range.
Burr coffee grinders are also more suited for keeping the flavor and aroma of the coffee beans intact, as they produce less heat from friction compared to blade grinders; “The oils and aromas can easily dissipate if the beans become too hot during grinding, although most grinders will not heat the beans to a high enough temperature to risk this occurring.”
Burr grinders obtain these lower speeds and even grind through two mechanisms. The lower cost models generally use a small electric motor to drive a series of reduction gears, while better constructed and more costly examples use a larger commercial motor and a belt, with no gear reduction to spin the burrs. The latter example is termed “direct drive”. The reduction gear versions are noisier and usually do not have the lifespan of the direct drive units.
Electrical powered burr grinders are available in many variations. Some grinders are “stepped” meaning that they are fixed by the factory into a set series of adjustments while “stepless” varieties use a worm drive or other mechanisms to offer a near-infinite number of adjustments within their grind range. Other variations include grinders that are equipped with dosers and others that are “doserless”. Dosers function as a catch bin to collect the ground coffee and by using a lever, users are able to dose a set amount of coffee. Doserless versions remove the bin and dosing function, and the grinder outputs the ground coffee directly into an espresso machine portafilter or into another container. The doserless examples normally feature additional functions such as weight based or advance time based grinding in order for a barista to grind for an exact amount of grounds required for a specific espresso shot.
Manual coffee grinders have been largely supplanted by electrically powered ones for speed. Manual grinders are used for convenience and aesthetic reasons and are usually less costly than electric models. An example is the manual Turkish coffee grinder; these are inexpensive and can grind coffee to fine powder for Turkish coffee.